B. Doloi

Enabling and Understanding Ultrasonic Machining of Engineering Ceramics Using Parametric Analysis

Ultrasonic machining (USM) on ceramics is highly demanded in the present industry because of its wide and potential uses in various fields in modern industries. Experiments based on central composite second-order rotatable design have been conducted on ultrasonic drilling of hexagonal shaped hole on high alumina ceramic. RSM was employed for developing empirical models. Analysis on machining characteristics of ultrasonic drilling operation was made based on the developed models. In this study, abrasive grit size, slurry concentration, power rating, tool feed rate, and slurry flow rate are considered as USM process parameters. The process performances on workpiece material with respect to material removal rate (MRR) and surface roughness are evaluated by using analysis of variance (ANOVA). The optimum parametric combination of USM process parameters for maximum MRR and minimum value of surface roughness have been obtained through multiobjective optimization.

Sidewall Insulation of Microtool for Electrochemical Micromachining to Enhance the Machining Accuracy

This paper presents a new approach for sidewall insulation of microtool by dip coating using liquid solution made of polymer and resin dissolved in isopropyl alcohol and use of acetone for opening the front end of the microtool. This method can also be used to remove the previously applied coat completely so that the microtool can be reinsulated again for the reuse. To investigate the effectiveness of insulating film, in-situ fabricated tungsten microtool of 104 µm diameter was insulated with 4.5-µm thick film by proposed method. Microfeatures like microhole and microgroove were machined by electrochemical micromachining (EMM) using uninsulated microtool and insulated microtool on stainless steel. The machining accuracy of the microfeatures machined were compared in terms of overcut and taper angle generated on microfeatures. In this way, 33.78% reduction in radial overcut of microhole and 58.64% reduction in width overcut of microgroove were observed. Taper angle was reduced from 40.57° to 18.00° and 58.39° to 25.20° for microhole and microgroove, respectively. The influence of sidewall insulation on shape accuracy, machining rate, and surface roughness of machined microfeatures was also investigated.

Experimental investigations into machining accuracy and surface roughness of microgrooves fabricated by electrochemical micromachining

Microgrooves are one of the basic microfeatures fabricated on different microproducts, used to integrate micro systems in various fields. Service life and product functioning of microproducts are directly influenced by shape, size, and surface quality of microgrooves fabricated on it. Hence, these are the important criteria to be considered while fabricating microgrooves on micro devices. This article presents the experimental study into fabrication of microgrooves on stainless steel by electrochemical micromachining. The influence of electrochemical micromachining process parameters like applied voltage, pulse frequency, duty ratio, electrolyte concentration, and microtool scanning speed on machining accuracy, that is, width overcut, length overcut and depth overcut, material removal rate, linearity of microgroove, depth profile, and surface finish were investigated during microgroove generation. From the experimental results, optimal parameters obtained were applied voltage of 2.6 V, pulse frequency of 8 MHz, 30% duty ratio, electrolyte concentration of 0.15 M H2SO4, and microtool scanning speed of 93.75 μm/s for machining of accurate microgroove, with best surface finish. Finally, microfeatures like “C”-shaped microgroove of rectangular cross section and multiple microgrooves as required in micro thermal devices have been machined with optimal parametric settings. This study will be useful for machining of need-based microgrooves on microproducts like micro actuators, micro pumps, micro coolers, and micromixers.

Optimisation of Nd:YAG laser micro–turning process using response surface methodology

The present paper investigates the laser micro–turning operation on cylindrical aluminium oxide (Al2O3) ceramic to study the influence of different process parameters namely, laser average power, pulse frequency, workpiece rotational speed, assist air pressure and Y feed rate on surface roughness (Ra and Rt) and micro–turning depth deviation. The mathematical models for the responses have been developed based on response surface methodology (RSM). Through different surface plots, analyses have been made to study the influences of process parameters on responses. The adequacy of the developed models has been tested through analysis of variance (ANOVA). To investigate into the variation in the output for small variations in significant process parameters, sensitivity analyses (SA) have been done of the models developed for each response. Multi–objective optimisation has also been performed for searching out the optimal parametric condition for achieving minimum surface roughness and minimum depth deviation during laser micro–turning process.

Analysis of surface characteristics of titanium during ECM

Surface phenomenon plays a decisive role in the pre-designed behaviour of titanium parts in a variety of applications. Titanium is extensively used in aerospace, defence, and biomedical applications. The human response to implanted titanium parts strongly related to the implant surface conditions. The aim of this paper is to present experimental investigation on electrochemically machined surface characteristics acquired on titanium, utilising developed cross flow electrolyte system. Effect of applied voltage across the tool and workpiece as well as electrolyte flow velocity during ECM process, for generation of different surface characteristics, has been successfully studied through experimentation. Attempt has been made to develop surface along with self-generated oxide layer, which facilitates in improving the corrosion and chemical resistance of titanium implant in biomedical application. The surface roughness ‘Rq’ of oxide layered machined surface obtained within 3.09 µm to 3.66 µm, which is within the range for functional attachment between bone and implant.

Fabrication of stepped hole on zirconia bioceramics by ultrasonic machining

ABSTRACT Zirconia (ZrO2) is a highly biocompatible ceramic material providing fracture strength properties that allow application as dental implants in biomedical engineering. In this present research, experimental analysis has been made for generating stepped hole on zirconia bioceramics with desired quality using ultrasonic machining (USM) process. Four independent controllable input process parameters are abrasive grain diameter, power rating, concentration of abrasive slurry, and tool feed rate. Material removal rate (MRR), overcut of larger diameter (OLD) hole, and overcut of smaller diameter (OSD) hole of stepped hole are considered as the responses. Response surface methodology (RSM) is used for modeling the performance of USM process. Multiobjective optimization has been performed to maximize the MRR and minimize the OLD hole and OSD hole of stepped holes. All the responses are improved at the optimal parametric condition and verified by confirmation test. The present research opens up the application feasibility of USM process for stepped hole generation on bioceramics and its utilization in biomedical field.

Multi-criteria optimization and predictive modeling of turning forces in high-speed machining of yttria based zirconia toughened alumina insert using desirability function approach

An attempt has been made to apply the Taguchi parameter design method and multi-response optimization using desirability analysis for optimizing the cutting conditions (cutting speed, feed rate and depth of cut) on machining forces while finish turning of AISI 4340 steel using developed yttria based zirconia toughened alumina inserts. These zirconia toughened alumina inserts were prepared through wet chemical co-precipitation route followed by powder metallurgy process. The L9 (4) orthogonal array of the Taguchi experiment is selected for three major parameters, and based on the mean response and signal-to-noise ratio of measured machining forces, the optimal cutting condition arrived for feed force is A1, B1 and C3 (cutting speed: 150 m/min, depth of cut: 0.5 mm and feed rate: 0.28 mm/rev) and for thrust and cutting forces is A3, B1 and C1 (cutting speed: 350 m/min, depth of cut: 0.5 mm and feed rate: 0.18 mm/rev) considering the smaller-the-better approach. Multi-response optimization using desirability function has been applied to minimize each response, that is, machining forces, simultaneously by setting a goal of highest cutting speed and feed rate criteria. From this study, it can be concluded that the optimum parameters can be set at cutting speed of 350 m/min, depth of cut of 0.5 mm and feed rate of 0.25 mm/rev for minimizing the forces with 78% desirability level.

Application of Back Propagation Neural Network Model for Predicting Flank Wear of Yttria Based Zirconia Toughened Alumina (ZTA) Ceramic Inserts

A back propagation neural network model has been adopted for the flank wear prediction of zirconia toughened alumina (ZTA) insert in turning operation. The experiments are performed on AISI 4340 steel using developed yttria based ZTA inserts. These inserts are prepared through wet chemical co-precipitation route followed by powder metallurgy process. Machining conditions such as cutting speed, feed rate and depth of cut are selected as input to the neural network model and flank wear of the inserts corresponding to these conditions has been chosen as the output of the network. The experimentally measured values are used to train the feed forward back propagation artificial neural network for prediction of those conditions. The convergence of the mean square error both in training and testing come out very well. The performance of the trained neural network has been validated with experimental data. The results demonstrate that the machining model is suitable and the optimization strategy satisfies practical requirements.

Pulsed Nd:YAG Laser Micro-turning Process of Alumina Ceramics

Laser micro-turning process is one of the new and emerging technologies in the area of laser material processing (LMP) of engineering materials. It is employed for generation of micro-turning surface of particular surface profile and dimensional accuracy on cylindrical workpiece with specific length and depth of turn within tight tolerance. As the process is recently developed micro manufacturing technique, a well planned research study and experimental investigation should be conducted considering various laser micro-turning process parameters. Therefore, various experimental schemes are adapted to study and analysis of significant process parameters on response criteria such as surface roughness and machining depth. A servo controller based fixture is designed and developed indigenously to hold and rotate the cylindrical shaped work samples at various workpiece rotating speed. Overlap between two successive spots (i.e. spot overlap) and overlap between two successive micro-groove widths (i.e. circumferential overlap) play major role for generating quality surface features during laser micro-turning process. Therefore, mathematical formulations of spot overlap and circumferential overlap are developed for better understanding of the laser micro-turning process and also to study the effects of these overlap factors on performance characteristics. Moreover, attempt has been made to carry out experimental investigation to micro-turn cylindrical shaped engineering ceramics at laser defocus conditions of laser beam. Moreover, comparative study and analyse is performed to explore the effect of focused and defocused conditions of laser beam on surface roughness criteria. SEM micrographs of the laser turned surface captured at various parametric combinations have also been studied for qualitative analysis of the process.

Optimisation of ECM process during machining of titanium using quality loss function

Titanium is used in different applications like aerospace, power generation, automotive and chemical industries. There are tremendous prospective for this material in dental, medical industries and biomedical engineering. It is found that processing of titanium has various tribulations when it is cut by conventional machining. Unconventional machining of titanium using EDM and LBM has their own limitations. Hence, attempt has made to process, this advance engineering material using electrochemical machining process. This paper presents experimental results based analysis of machining-characteristics during electrochemical machining of titanium material. These results are obtained on commercially pure titanium, utilising indigenously developed cross flow electrolyte supply system. Parametric analysis and single objective optimisation has carried out based on Taguchi methodology. Multi-objective optimisation has also been made using quality loss function. Mathematical models are developed to establish the relationship between various significant process parameters and machining performance criteria during ECM. The ANOVA result shows that electrolyte flow rate, applied voltage, electrolyte concentration and initial inter-electrode gap (IIEG) are the major contributing parameters to affect machining criteria like material removal rate and surface roughness of ECM-ed titanium work sample.